1. Field of the Invention
The present invention relates to a cleaning device, and an image forming apparatus incorporated with the cleaning device.
2. Description of the Related Art
Heretofore, an amorphous silicon photosensitive drum has been used in an image forming apparatus. Amorphous silicon to be used as a material for the amorphous silicon photosensitive drum has a relatively large hardness and a long useful life, but has a disadvantage that an electric charge is likely to leak during a long-term use, thereby deteriorating a toner image. In view of the above, there is known a cleaning device equipped with a cleaning roller i.e. a contact roller. Specifically, the cleaning roller is constantly pressingly contacted with the surface of the photosensitive drum to thereby polish the surface of the photosensitive drum. The cleaning roller is made of a foaming synthetic rubber e.g. EPDM (ethylene propylene diene terpolymer).
Japanese Unexamined Patent Publication No. 2006-201333 (D1) discloses an image forming apparatus, wherein a sheet transport path extends substantially horizontally in a tangential direction with respect to a top of a photosensitive drum. In the apparatus disclosed in D1, a cleaning roller is pressingly contacted with the surface of the photosensitive drum at a vertically mid point of the cleaning roller and a vertically mid point of the photosensitive drum substantially horizontally. The photosensitive drum and the cleaning roller are each rotated in a downward direction at a pressing contact position i.e. a nip position between the photosensitive drum and the cleaning roller. With this arrangement, an upper end of a vertically extending cleaning blade is pressingly contacted with the photosensitive drum at a position lower than the nip position i.e. downstream with respect to the rotating direction of the drum. A cleaning device having the above arrangement is e.g. disclosed in Japanese Unexamined Patent Publication No. 2005-148609 (D2).
Although D2 does not disclose such an arrangement, a cleaning device generally has a housing, and a cleaning roller is provided in the housing. Also, a cleaning blade is provided in the housing. If a function of collecting toner scraped from the surface of the photosensitive drum is required, a spiral roller for collecting the toner is also provided in the housing.
In the cleaning device, toner added with a polishing agent such as titanium oxide is used to polish the surface of the photosensitive drum. Primary part of the toner scraped from the surface of the photosensitive drum by the cleaning roller and the cleaning blade is allowed to fall onto a bottom surface in the housing. On the other hand, the toner that has been adhered to the outer surface of the cleaning roller is carried to the nip position between the photosensitive drum and the cleaning roller by rotation of the cleaning roller, and the surface of the photosensitive drum is polished at the nip position by the toner adhered to the outer surface of the cleaning roller. However, since the amount of toner that has been adhered to the outer surface of the cleaning roller is meager, the surface of the photosensitive drum may not be sufficiently polished as required.